Help With Laying Out Ordinates (Warbird Replica Project)

[VCS1]

Hello,
I have previously posted about my attempts to build a replica P-35A. I am in the need of help. I am trying to build vertical stabilizer ribs (per B/P) and I am having difficulty laying out the ordinates (Width of ribs in this case). I have studied lofting the fuselage, but wing and rib lay outs are a new area for me. I appreciate general information from those who have faced this same problem with other aircraft (the NA P-51 uses ordinate based drawings I know for a fact) and perhaps their approach to laying out sheetmetal parts such as these. FYI, this is scratch built project so I do not have any patterns to reference, just the B/P's. I will be later transfering all this information to a 3D cad model, but I like to get a general idea of what I am trying to do on paper first. Thanks for any and all help the WIX can provide!!

[visaliaaviation]

I can probably give some pointers. Feel free to contact me on Private Message.

visaliaaviation

[Nathan]

hi VCS1

Haven't heard from you in awhile. Its a shame you live in California casue I would be there helping you out every day if I could.....love the P-35A....keep us updated on it. .... email me at warhawknm@yahoo.com.

Good luck with everything..

cheers,
Nathan

[Warbird Kid]

Likewise, Im here in Connecticut, but i would gladly aid you in a repro of this awesome fighter!! Just move your little operation to the east coast!!

Let us know whats going on.

All the best,
Chris

[Cvairwerks]

V: The ordinate system is pretty easy. Think back to junior high math and learning to plot curves. The basic layout is that one column gives you the distance along the chord from the datum and the other tells you how far from the chord the surface line is at that point. If the airfoil is symetrical, the table will only give you one pair of numbers. If it's not a symetrical shape, there will be a third column of numbers that apply to the other surface. The chord dimension will either be in a decimal number or a percentage. You will have to figure that out from the drawing. Also verify if the tables are using the airfoil centerline or MAC for the reference.
Once you have the data plotted, its just drawing the best fit, smoothest curve between all the points.

There are numerous books on aircraft lofting, but also look at lofting and working with tables of offsets from boats.

If I remember correctly "Theory of Wing Sections" has some good info on how this all works and a bunch of good data in the referenyou have your CAD routine, it's easy to draw using copy and offsets. Draw a horizontal centerline. Draw a vertical centerline. Making the assumption that the the nose point is the datum, and that your data is in decimal form, copy the vertical line and place it offset to the right by the distance given in the table for the second point on the rib. You've now done half the locating for the point. Repeat the process for all of the vertical dimensions. Repeat the process for the other column, but use the horizontal line for the offsets. Repeat the offset above and below the centerline.

As you work across the airfoil, trim your verticals and horiozontals so that you end up with stairstepping across the drawing. Draw a curve via intersection points using the pick feature so that you go through the intersection, and make it a polyline. Connect the top and bottom surfaces, get rid of your construction lines and you've electonically lofted the rib surface. Now all you have to do is calculate the bend allowance and reductions and flange width and add the appropriate offset to the profile, and you have a basic sheetmetal pattern.

You can do the same thing by hand drawing, but the curve fitting will have to be done with french curves and flexible curves. It's a bit harder and more tedious to do it by hand and get it right. It's also terribly time consuming too. I did a fairly simple transonic wind tunnel model for a research program and even doing the drawings at 20 times size, I had over 200 manhours in the basic model of a wing section. By the time you add the instrumentation drawings, I belive I was over 300 hours on those 10 "E" sized pages.

[mustanglover]

Very good trying to explain that, I understand what you are saying, but I do it all the time too, for the last 20 years..........went from pen and ink to CAD.

I can think of no other way to put it into words. Recently I have been putting NA T-6/SNJ drawings into CAD, but the problems I have seen is knowing what they mean in some areas of the original drawings. You really have to understand the basics of drawing conventions and then think really hard about how they did it back then.

I also enjoy taking a part or shape and doing it backwards so to speak. I draw and plot out a grid. Then take the part/shape and lay it down on the grid, trace it out and then measure the X and Y coordinates and "draw" into CAD. Kinda fun stuff.

V: The ordinate system is pretty easy. Think back to junior high math and learning to plot curves. The basic layout is that one column gives you the distance along the chord from the datum and the other tells you how far from the chord the surface line is at that point. If the airfoil is symetrical, the table will only give you one pair of numbers. If it's not a symetrical shape, there will be a third column of numbers that apply to the other surface. The chord dimension will either be in a decimal number or a percentage. You will have to figure that out from the drawing. Also verify if the tables are using the airfoil centerline or MAC for the reference.
Once you have the data plotted, its just drawing the best fit, smoothest curve between all the points.

There are numerous books on aircraft lofting, but also look at lofting and working with tables of offsets from boats.

If I remember correctly "Theory of Wing Sections" has some good info on how this all works and a bunch of good data in the referenyou have your CAD routine, it's easy to draw using copy and offsets. Draw a horizontal centerline. Draw a vertical centerline. Making the assumption that the the nose point is the datum, and that your data is in decimal form, copy the vertical line and place it offset to the right by the distance given in the table for the second point on the rib. You've now done half the locating for the point. Repeat the process for all of the vertical dimensions. Repeat the process for the other column, but use the horizontal line for the offsets. Repeat the offset above and below the centerline.

As you work across the airfoil, trim your verticals and horiozontals so that you end up with stairstepping across the drawing. Draw a curve via intersection points using the pick feature so that you go through the intersection, and make it a polyline. Connect the top and bottom surfaces, get rid of your construction lines and you've electonically lofted the rib surface. Now all you have to do is calculate the bend allowance and reductions and flange width and add the appropriate offset to the profile, and you have a basic sheetmetal pattern.

You can do the same thing by hand drawing, but the curve fitting will have to be done with french curves and flexible curves. It's a bit harder and more tedious to do it by hand and get it right. It's also terribly time consuming too. I did a fairly simple transonic wind tunnel model for a research program and even doing the drawings at 20 times size, I had over 200 manhours in the basic model of a wing section. By the time you add the instrumentation drawings, I belive I was over 300 hours on those 10 "E" sized pages.

[Cvairwerks]

V: Yep, didn't do the pen and ink thing, but lots of board work and some reversed Velum stuff too. The big problem with drawing conventions is that every company has there own from that time period, and they were somewhat lax in enforcing it on all the designers and drafters. Basic info for the drawing should be pretty standard for the entire aircraft. Title blocks, limitation blocks ect... Where the bugaboo starts is how a particular drafter lays out and presents the part. A good one will present a drawing in such a form that a fabricator can pick it up, read all necessary info for the part and be able to create it without having to dive into the books or refernce materails. Where things get wacky is where the drafter used awkward reference points or lines to create the part.

What I try to do with old drawings that are kinda rough, is to try and recreate the part as much as possible from the readily findable data. After that, I start trying to track down the missing data. I can usually develope a lot of the data on the fly just because I'm used to working with prints that run up to 40 or 50 pages on an assembly and I'm 5th generation machinist/fabircator in the family.

If you have some specific questions, toss them out and I'll bet we can come up the answer from somewhere in the group.

I don't have any standards manuals that would help. Maybe BDK knows of some.

[TAdan]

V: The big problem with drawing conventions is that every company has there own from that time period, and they were somewhat lax in enforcing it on all the designers and drafters. part.

.

Hence the reason Im on WIX all day (Another CAD guy)

[visaliaaviation]

Cvairwerks wrote: "Making the assumption that the the nose point is the datum" and "Where things get wacky is where the drafter used awkward reference points or lines to create the part."

Skininng and structural considerations are probably more specific to your re-creation needs than anything else. If a flat wing skin attaches to a spar or a stringer, that is probably a "straight line" in all views and can play havoc with one's understanding of what is considered"normal". Points of reference are whatever the engineer or draftman used. Conventions for universal drafting practices were not established until somewhat later than P-35 and majority of WWII types.

Since you mentioned Mustangs, fin/rudder use rudder hing line for chordwise reference, as does the horizontal stab and elevators. Wing uses constant 25% line. But what about flap and aileron hing lines? do they fall on "normal" transition lines?? Washout??? Semi eliptical plan forms????

[VCS1]

Hello,
I first of all wanted to thank everyone who responded for my request for help. The WIX is becoming as much of a "tool" in my tool box as my rivet gun!! The collection of knowledge and the willingness to share it by those who respond is amazing.

Secondly I would like to acknowledge my gratitude to "visaliaaviation", Mr. Charlie Neely. I grew up in the same central California area that Charlie lives in. As a young kid (like most on the WIX) I was very interested in warbirds. I sought out anybody that could learn from while attending A&P school and afterward as I started my first Vultee BT-13 project. Through a mutual friend I was put in contact with Charlie. He very graciously loaned me many manuals, documents and gave me advice regarding vintage aircraft design and construction, particularly the P-51 Mustang. It was him who also first told be about lofting and its capabilities for building aircraft. He even gave me a free copy of his highly detailed (and prized) drawings of the P-51. Charlie is a very modest man , most probably don't know his drawings have been featured in the book "Mustang Designer" by Ray Wagner (Charlie even autographed my copy). Alot of people would not have taken the time for "some kid". I hope Charlie's investment in me pays off with this P-35A project.

[VCS1]

Hello,
I am going to post the ordinates for the first vertical stab rib I am laying out (station 14 1/8). Without posting the actual drawing here are the basics:

1. .032 24ST Alclad skin thickness
2. 26 23/32 in Rib total length
3. Distance from LE (Leading Edge) to beginning of rib on DWG 22.576
4. LE Radius .122
5. Beginning and End of rib shown on DWG as having 2 degrees of angle
6. 11/16 inch flanges with 3/32 bend radius

Here is the "Ordinates Table"

A (From LE) B (Ord) C (Angle)
1.009 - .860 - N/A
2.018 - 1.395 - N/A
4.036 - 2.317 - N/A
6.054 - 2.978 - N/A
8.072 - 3.507 - N/A
12.107 - 4.173 - N/A
16.143 - 4.578- N/A
20.179 - 4.766- N/A
24.215 - 4.828 - 3 degrees
32.287 -4.688 - 2 degrees
40.359 -4.260 - 1 degree
48.431 -3.672 - 0 degree
56.503 - 2.948- N/A

Thanks again for the advice and help. I hope to establish all the dimensions to began this project soon.

[Rossco]

Cad is fine for 2D but parametric 3D ones are the go.There are Naca profile generator programs online if you can find them to help you with the wings.Start off with the major structures and work your way up off from there..
http://www.spitfireprojecta58-27.com/MK ... efault.htm
Check out the 3d design page.

[visaliaaviation]

Dave, is that you? I totally missed the P-35 connection! Contact me on PM or e-mail at packardpursuit@yahoo.com
Charlie

[VCS1]

Just wanted to post an update to my request. I really appreciated the advise about how to lay the vertical rib. I have now completed the first of many ribs to be fabricated for this project. I temporarily attached it (minus the vertical spars) to the aft P-35A mockup I have constructed. I will post more pictures here on the WIX and my website, www.P-35.com as I make progress on the project.

[bdk]

That looks fantastic! What did you use as a form block? Have you heat treated the rib already after forming?